Desynchronization algorithms are essential in the design of collision-free medium access control (MAC) mechanisms for wireless sensor networks. Desync is a well-known desynchronization algorithm that operates under limited listening. In this paper, we view Desync as a gradient descent method solving a convex optimization problem. This enables the design of a novel decentralized, collision-free, multichannel medium access control (MAC) algorithm. Moreover, by using Nesterov's fast gradient method, we obtain a new algorithm that converges to the steady network state much faster. Simulations and experimental results on an IEEE 802.15.4-based wireless sensor network deployment show that our algorithms achieve significantly faster convergence to steady network state and substantially higher throughput compared to the recently standardized IEEE 802.15.4e-2012 time synchronized channel hopping (TSCH) scheme. In addition, our mechanism has a comparable power dissipation with respect to TSCH and does not need a coordinator node or coordination channel.

We are working on a new concept for decentralized medium access control (MAC), termed decentralized time-synchronized channel swapping (DT-SCS). Under the proposed DT-SCS and its associated MAC-layer protocol, wireless nodes converge to synchronous beacon packet transmissions across all IEEE802.15.4 channels, with balanced numbers of nodes in each channel. This is achieved by reactive listening mechanisms, based on pulse coupled oscillator techniques. Once convergence to the multichannel time-synchronized state is achieved, peer-to-peer channel swapping can then take place via swap requests and acknowledgments made by concurrent transmitters in neighboring channels. Our implementation of DT-SCS reveals that our proposal comprises an excellent candidate for completely decentralized MAC-layer coordination in WSNs by providing for quick convergence to steady state, high bandwidth utilization, high connectivity and robustness to interference and hidden nodes. The demo will showcase the properties of DT-SCS and will also present its behaviour under various scenarios for hidden nodes and interference, both experimentally and with the help of visualization of simulation results.

Distributed desynchronization algorithms are key to wireless sensor networks as they allow for medium access control in a decentralized manner. In this paper, we view desynchronization primitives as iterative methods that solve optimization problems. In particular, by formalizing a well established desynchronization algorithm as a gradient descent method, we establish novel upper bounds on the number of iterations required to reach convergence. Moreover, by using Nesterov's accelerated gradient method, we propose a novel desynchronization primitive that provides for faster convergence to the steady state. Importantly, we propose a novel algorithm that leads to decentralized time-synchronous multichannel TDMA coordination by formulating this task as an optimization problem. Our simulations and experiments on a densely-connected IEEE 802.15.4-based wireless sensor network demonstrate that our scheme provides for faster convergence to the steady state, robustness to hidden nodes, higher network throughput and comparable power dissipation with respect to the recently standardized IEEE 802.15.4e-2012 time-synchronized channel hopping (TSCH) scheme.

Future deployments of wireless sensor network (WSN) infrastructures for environmental or event monitoring are expected to be equipped with energy harvesters (e.g. piezoelectric, thermal, photovoltaic) in order to substantially increase their autonomy. In this paper we derive conditions for energy neutrality, i.e. perpetual energy autonomy per sensor node, by balancing the node's expected energy consumption with its expected energy harvesting capability. Our analysis assumes a uniformly-formed WSN, i.e. a network comprising identical transmitter sensor nodes and identical receiver/relay sensor nodes with a balanced cluster-tree topology. The proposed framework is parametric to: (i) the duty cycle for the network activation; (ii) the number of nodes in the same tier of the cluster-tree topology; (iii) the consumption rate of the receiver node(s) that collect (and possibly relay) data along with their own; (iv) the marginal probability density function (PDF) characterizing the data transmission rate per node; (v) the expected amount of energy harvested by each node. Based on our analysis, we obtain the number of nodes leading to the minimum energy harvestingrequirement for each tier of the WSN cluster-tree topology. We also derive closed-form expressions for the difference in the minimum energy harvesting requirements between four transmission rate PDFs in function of the WSN parameters. Our analytic results are validated via experiments using TelosB sensor nodes and an energy measurement testbed. Our framework is useful for feasibility studies on energy harvesting technologies in WSNs and for optimizing the operational settings of hierarchical WSN-based monitoring infrastructures prior to time-consuming testing and deployment within the application environment.